Conventionally, as a mobile router device and a home agent device, for example, there exist the ones as disclosed in a specification of U.S. Patent Application No. 2003-0117965. FIG. 15 shows a configuration of a communication network including the conventional mobile router device and the home agent device disclosed in the specification of U.S. Patent Application No. 2003-0117965.
In FIG. 15, a mobile router device (MR) 1801 and a mobile node (MN) 1802 leave a home link 1805 in a state of forming a mobile network 1811 and are connected to a foreign link 1808. Then, the mobile router device (MR) 1801 generates a care-of address based on a router advertisement message (hereinafter, written as “RA message”) received from an access router device (AR) 1807 on the foreign link 1808.
Next, the mobile router device 1801 trades a binding update message (hereinafter, written as “BU message”) and the like with a home agent device (HA) 1804, and the home agent device 1804 creates a binding cache. Further, the home agent device 1804 creates a bi-directional tunnel between the home agent device 1804 and the mobile router device 1801.
After the bi-directional tunnel is created, the mobile router device 1801 transmits routing information to the home agent device 1804. Then, the home agent device 1804 interprets the routing information and multicasts the routing information to the home link 1805.
Accordingly, a packet addressed to the mobile node (MN) 1802 from a correspondent node (CN) 1810 connecting to an internet 1809 are relayed from a router 1806 on the home link 1805 to the home agent device 1804, and further, transferred to the mobile router device 1801 using the bi-directional tunnel.
Then, the mobile router device 1801 relayed the transferred packet to the mobile node 1802 in the mobile network 1811.
Hereupon, a data configuration of an NEMO binding update message is shown in FIG. 8, which is disclosed in an IETF Mobile IP WG internet draft “Network Mobility (NEMO) Basic Support Protocol”. Note that the NEMO binding update message is formed by extending a mobile IPv6 binding update message disclosed in an IETF Mobile IP WG internet draft “Mobility Support in IPv6”.
In FIG. 8, when transmitted from the mobile router device 1801 in a movement destination to the home agent device 1804, a care-of address of the mobile router device 1801 is set in a source address 801, and a global address of the home agent device 1804 is set in a destination address 802. And a home address of the mobile router device 1801 is set in a home address 803 of a destination option header. Further, the care-of address of the mobile router device 1801 is set in a proxy care-of address 804 of a mobility header, and valid time of these information is set in units of seconds in a lifetime 805.
The home agent device 1804 registers the care-of address in the binding cache, associating it with the home address of the mobile router device 1801 based on these information. FIG. 7A is a binding cache table showing a data structure of information registered in the binding cache.
In FIG. 7A, according to a home address 701, a registered mobile router device is specified, and associated with a care-of address 702 in the foreign link where the mobile router is currently located. Further, a prefix 703 showing a network address unit of a mobile network to which the mobile router device belongs and a valid time 704 showing available duration of the mobile router device are registered, being associated with the home address 701.
However, when the mobile router device 1801 is replaced with another mobile router device, it is necessary that the BU message in which “0” is set in the lifetime 805 is sent to the home agent device 1804 from the previously used mobile router device 1801 to delete data registered in the binding cache. However, the mobile router device 1801 can not send the BU message to the home agent device 1804 when it has already cut the connection to the foreign link. Thus, the home agent device continues sending messages addressed to the mobile node which was previously under the mobile router device 1801 to the mobile router device 1801 in accordance with information registered in the binding cache until the time which has been set in the lifetime 805 has passed. However, the mobile router device 1801 is not connected to the foreign link 1808, the transmitted packets do not reach the mobile node 1802 and vanish.